The development and regulation of neurochemical mechanisms underlying synaptic transmission will be examined to gain information about processes governing formation and long-term modulation of synapses. These events will be studied in dissociated cell cultures prepared from embryonic chick spinal cord and muscle. The major focus of the proposal will be to examine the development of cholinergic neurons with respect to their capacity to synthesize, store, and release ACh, and to determine how these properties depend on muscle influence. Neuronal influences on muscle ACh receptor distribution and number as a consequence of synapse formation will also be examined. High affinity choline uptake by spinal cord cells in culture will be studied to assess whether it is restricted to cholinergic neurons under these conditions, and if so, whether it can be used to identify cholinergic neurons and follow their development. BIBLIOGRAPHIC REFERENCES: Berg, D. K. and Hall, Z.W. (1975) Increased extrajunctional acetylcholine sensitivity produced by chronic prostsynaptic neuromuscular blockage. J. Physiol. 244: 659-676. Berg, D.K. and Hall, Z.W. (1975) Loss of alpha-bungarotoxin from junctional and extrajunctional acetylcholine receptors in rat diaphragm muscle in vivo and in organ culture. J. Physiol. 255: 771-789.